1. Field of the Invention
This invention relates to a chemically amplified positive resist composition which is highly sensitive to high energy radiation such as deep-ultraviolet ray, electron beam and X-ray, can be developed with alkaline aqueous solution to form a pattern, and is thus suitable for use in a fine patterning technique.
2. Prior Art
As the LSI technology tends toward higher integration and higher speed, further refinement of pattern rules is required. The current patterning technology mostly relies on light exposure which is now approaching to the essential limit of resolution which is dictated by the wavelength of a light source. It is generally recognized that in light exposure using g-line (wavelength 436 nm) or i-line (wave-length 365 nm) as a light source, a pattern rule of about 0.5 .mu.m is the limit. For LSIs fabricated by such light exposure technique, a degree of integration equivalent to 16 mega-bit DRAM is the limit. At present, LSIs fabricated in the laboratory have reached this stage. It is urgently required to develop a finer patterning technique.
Under such circumstances, deep-ultraviolet lithography is regarded promising as the next generation of fine patterning technology. The deep-UV lithography is capable of working on the order of 0.3 to 0.4 .mu.m. If a less light absorbing resist is used, it is possible to form a pattern having a side wall nearly perpendicular to the substrate.
Recently developed were chemically amplified positive working resist materials using acid catalysts as disclosed in JP-B 27660/1990, JP-A 27829/1988, U.S. Pat. No. 4,491,628 and 5,310,619. These materials are promising resist materials especially suited for deep-UV lithography since they allow a high intensity KrF excimer laser to be utilized as a deep-UV light source and have high sensitivity, resolution and dry etching resistance.
Prior art chemically amplified positive resists, however, suffer from the problem known as post-exposure delay (PED) that when deep-UV, electron beam or X-ray lithography is carried out, line patterns would have a T-top configuration, that is, patterns become thick at the top if the leave-to-stand or delay time from exposure to post-exposure baking (PEB) is extended. There also arises a "skirting" phenomenon that the pattern is widened at the bottom because a portion of the resist in contact with the substrate is incompletely dissolved and left upon development. These problems not only make difficult dimensional control in the lithographic process, but also adversely affect dimensional control in the processing of substrates using dry etching. In this regard, reference is made to W. Hinsberg et al., J. Photopolym. Sci. Technol., 6 (4), 535-546 (1993) and T. Kumada et al., J. Photopolym., Sci. Technol., 6 (4), 571-574 (1993). There are available no chemically amplified positive resists which can solve these problems and are thus practically acceptable.
It is understood for these chemically amplified positive resist materials that basic compounds in the air largely participate in the PED problem and basic compounds on the substrate surface largely participate in the skirting phenomenon. Light exposure generates acids at the resist surface which react with basic compounds in the air and also with basic compounds on the substrate surface at the junction between the resist and the substrate and are thereby deactivated. Then insolubilized layers are formed at the resist and substrate surfaces, resulting in T-top configured and skirting patterns.
It is known from JP-A 232706/1993 and 249683/1993 that addition of a basic compound to the resist material suppresses the influence of basic compounds in the air and is also effective for solving the PED problem. However, the basic compound used therein is little taken into the resist film due to volatilization, less compatible with resist components, and unevenly dispersible in a resist film. Thus the basic compound cannot achieve its advantages in a reproducible manner and causes a drop of resolving power.
It is believed that the skirting phenomenon occurs because the pattern profile largely depends on a substrate and especially when the substrate is a nitride film, N-H bonds in the nitride film deactivate acid at the chemically amplified resist/nitride film substrate interface. This problem can be solved by treating a nitride film with an oxygen plasma and an acid chemical (see Usujima et al., Preprint of 1994 Spring Meeting of Applied Physical Society, page 566, 29a, MB-10). This process requires an oxygen plasma generating system which is very expensive.
There is a strong demand for a chemically amplified positive working resist material which is improved in dimensional precision.